RFC 7591

OAuth 2.0 Dynamic Client Registration Protocol

3. Client Registration Endpoint
The client registration endpoint is an OAuth 2.0 endpoint defined in
this document that is designed to allow a client to be registered
with the authorization server. The client registration endpoint MUST
accept HTTP POST messages with request parameters encoded in the

entity body using the "application/json" format. The client
registration endpoint MUST be protected by a transport-layer security
mechanism, as described in Section 5.
The client registration endpoint MAY be an OAuth 2.0 [RFC6749]
protected resource and it MAY accept an initial access token in the
form of an OAuth 2.0 access token to limit registration to only
previously authorized parties. The method by which the initial
access token is obtained by the client or developer is generally out
of band and is out of scope for this specification. The method by
which the initial access token is verified and validated by the
client registration endpoint is out of scope for this specification.
To support open registration and facilitate wider interoperability,
the client registration endpoint SHOULD allow registration requests
with no authorization (which is to say, with no initial access token
in the request). These requests MAY be rate-limited or otherwise
limited to prevent a denial-of-service attack on the client
registration endpoint.
3.1. Client Registration Request
This operation registers a client with the authorization server. The
authorization server assigns this client a unique client identifier,
optionally assigns a client secret, and associates the metadata
provided in the request with the issued client identifier. The
request includes any client metadata parameters being specified for
the client during the registration. The authorization server MAY
provision default values for any items omitted in the client
metadata.
To register, the client or developer sends an HTTP POST to the client
registration endpoint with a content type of "application/json". The
HTTP Entity Payload is a JSON [RFC7159] document consisting of a JSON
object and all requested client metadata values as top-level members
of that JSON object.
For example, if the server supports open registration (with no
initial access token), the client could send the following
registration request to the client registration endpoint.

The following is a non-normative example request not using an initial
access token:
POST /register HTTP/1.1
Content-Type: application/json
Accept: application/json
Host: server.example.com
{
"redirect_uris": [
"https://client.example.org/callback",
"https://client.example.org/callback2"],
"client_name": "My Example Client",
"client_name#ja-Jpan-JP":
"\u30AF\u30E9\u30A4\u30A2\u30F3\u30C8\u540D",
"token_endpoint_auth_method": "client_secret_basic",
"logo_uri": "https://client.example.org/logo.png",
"jwks_uri": "https://client.example.org/my_public_keys.jwks",
"example_extension_parameter": "example_value"
}
Alternatively, if the server supports authorized registration, the
developer or the client will be provisioned with an initial access
token. (The method by which the initial access token is obtained is
out of scope for this specification.) The developer or client sends
the following authorized registration request to the client
registration endpoint. Note that the initial access token sent in
this example as an OAuth 2.0 Bearer Token [RFC6750], but any OAuth
2.0 token type could be used by an authorization server.

The following is a non-normative example request using an initial
access token and registering a JWK Set by value (with line breaks
within values for display purposes only):
POST /register HTTP/1.1
Content-Type: application/json
Accept: application/json
Authorization: Bearer ey23f2.adfj230.af32-developer321
Host: server.example.com
{
"redirect_uris": ["https://client.example.org/callback",
"https://client.example.org/callback2"],
"client_name": "My Example Client",
"client_name#ja-Jpan-JP":
"\u30AF\u30E9\u30A4\u30A2\u30F3\u30C8\u540D",
"token_endpoint_auth_method": "client_secret_basic",
"policy_uri": "https://client.example.org/policy.html",
"jwks": {"keys": [{
"e": "AQAB",
"n": "nj3YJwsLUFl9BmpAbkOswCNVx17Eh9wMO-_AReZwBqfaWFcfG
HrZXsIV2VMCNVNU8Tpb4obUaSXcRcQ-VMsfQPJm9IzgtRdAY8NN8Xb7PEcYyk
lBjvTtuPbpzIaqyiUepzUXNDFuAOOkrIol3WmflPUUgMKULBN0EUd1fpOD70p
RM0rlp_gg_WNUKoW1V-3keYUJoXH9NztEDm_D2MQXj9eGOJJ8yPgGL8PAZMLe
2R7jb9TxOCPDED7tY_TU4nFPlxptw59A42mldEmViXsKQt60s1SLboazxFKve
qXC_jpLUt22OC6GUG63p-REw-ZOr3r845z50wMuzifQrMI9bQ",
"kty": "RSA"
}]},
"example_extension_parameter": "example_value"
}
3.1.1. Client Registration Request Using a Software Statement
In addition to JSON elements, client metadata values MAY also be
provided in a software statement, as described in Section 2.3. The
authorization server MAY ignore the software statement if it does not
support this feature. If the server supports software statements,
client metadata values conveyed in the software statement MUST take
precedence over those conveyed using plain JSON elements.
Software statements are included in the requesting JSON object using
this OPTIONAL member:
software_statement
A software statement containing client metadata values about the
client software as claims. This is a string value containing the
entire signed JWT.

In the following example, some registration parameters are conveyed
as claims in a software statement from the example in Section 2.3,
while some values specific to the client instance are conveyed as
regular parameters (with line breaks within values for display
purposes only):
POST /register HTTP/1.1
Content-Type: application/json
Accept: application/json
Host: server.example.com
{
"redirect_uris": [
"https://client.example.org/callback",
"https://client.example.org/callback2"
],
"software_statement": "eyJhbGciOiJSUzI1NiJ9.
eyJzb2Z0d2FyZV9pZCI6IjROUkIxLTBYWkFCWkk5RTYtNVNNM1IiLCJjbGll
bnRfbmFtZSI6IkV4YW1wbGUgU3RhdGVtZW50LWJhc2VkIENsaWVudCIsImNs
aWVudF91cmkiOiJodHRwczovL2NsaWVudC5leGFtcGxlLm5ldC8ifQ.
GHfL4QNIrQwL18BSRdE595T9jbzqa06R9BT8w409x9oIcKaZo_mt15riEXHa
zdISUvDIZhtiyNrSHQ8K4TvqWxH6uJgcmoodZdPwmWRIEYbQDLqPNxREtYn0
5X3AR7ia4FRjQ2ojZjk5fJqJdQ-JcfxyhK-P8BAWBd6I2LLA77IG32xtbhxY
fHX7VhuU5ProJO8uvu3Ayv4XRhLZJY4yKfmyjiiKiPNe-Ia4SMy_d_QSWxsk
U5XIQl5Sa2YRPMbDRXttm2TfnZM1xx70DoYi8g6czz-CPGRi4SW_S2RKHIJf
IjoI3zTJ0Y2oe0_EJAiXbL6OyF9S5tKxDXV8JIndSA",
"scope": "read write",
"example_extension_parameter": "example_value"
}
3.2. Responses
Upon a successful registration request, the authorization server
returns a client identifier for the client. The server responds with
an HTTP 201 Created status code and a body of type "application/json"
with content as described in Section 3.2.1.
Upon an unsuccessful registration request, the authorization server
responds with an error, as described in Section 3.2.2.
3.2.1. Client Information Response
The response contains the client identifier as well as the client
secret, if the client is a confidential client. The response MAY
contain additional fields as specified by extensions to this
specification.

client_id
REQUIRED. OAuth 2.0 client identifier string. It SHOULD NOT be
currently valid for any other registered client, though an
authorization server MAY issue the same client identifier to
multiple instances of a registered client at its discretion.
client_secret
OPTIONAL. OAuth 2.0 client secret string. If issued, this MUST
be unique for each "client_id" and SHOULD be unique for multiple
instances of a client using the same "client_id". This value is
used by confidential clients to authenticate to the token
endpoint, as described in OAuth 2.0 [RFC6749], Section 2.3.1.
client_id_issued_at
OPTIONAL. Time at which the client identifier was issued. The
time is represented as the number of seconds from
1970-01-01T00:00:00Z as measured in UTC until the date/time of
issuance.
client_secret_expires_at
REQUIRED if "client_secret" is issued. Time at which the client
secret will expire or 0 if it will not expire. The time is
represented as the number of seconds from 1970-01-01T00:00:00Z as
measured in UTC until the date/time of expiration.
Additionally, the authorization server MUST return all registered
metadata about this client, including any fields provisioned by the
authorization server itself. The authorization server MAY reject or
replace any of the client's requested metadata values submitted
during the registration and substitute them with suitable values.
The client or developer can check the values in the response to
determine if the registration is sufficient for use (e.g., the
registered "token_endpoint_auth_method" is supported by the client
software) and determine a course of action appropriate for the client
software. The response to such a situation is out of scope for this
specification but could include filing a report with the application
developer or authorization server provider, attempted re-registration
with different metadata values, or various other methods. For
instance, if the server also supports a registration management
mechanism such as that defined in [RFC7592], the client or developer
could attempt to update the registration with different metadata
values. This process could also be aided by a service discovery
protocol, such as [OpenID.Discovery], which can list a server's
capabilities, allowing a client to make a more informed registration
request. The use of any such management or discovery system is
optional and outside the scope of this specification.

The successful registration response uses an HTTP 201 Created status
code with a body of type "application/json" consisting of a single
JSON object [RFC7159] with all parameters as top-level members of the
object.
If a software statement was used as part of the registration, its
value MUST be returned unmodified in the response along with other
metadata using the "software_statement" member name. Client metadata
elements used from the software statement MUST also be returned
directly as top-level client metadata values in the registration
response (possibly with different values, since the values requested
and the values used may differ).
The following is a non-normative example response of a successful
registration:
HTTP/1.1 201 Created
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache
{
"client_id": "s6BhdRkqt3",
"client_secret": "cf136dc3c1fc93f31185e5885805d",
"client_id_issued_at": 2893256800,
"client_secret_expires_at": 2893276800,
"redirect_uris": [
"https://client.example.org/callback",
"https://client.example.org/callback2"],
"grant_types": ["authorization_code", "refresh_token"],
"client_name": "My Example Client",
"client_name#ja-Jpan-JP":
"\u30AF\u30E9\u30A4\u30A2\u30F3\u30C8\u540D",
"token_endpoint_auth_method": "client_secret_basic",
"logo_uri": "https://client.example.org/logo.png",
"jwks_uri": "https://client.example.org/my_public_keys.jwks",
"example_extension_parameter": "example_value"
}
3.2.2. Client Registration Error Response
When an OAuth 2.0 error condition occurs, such as the client
presenting an invalid initial access token, the authorization server
returns an error response appropriate to the OAuth 2.0 token type.

When a registration error condition occurs, the authorization server
returns an HTTP 400 status code (unless otherwise specified) with
content type "application/json" consisting of a JSON object [RFC7159]
describing the error in the response body.
Two members are defined for inclusion in the JSON object:
error
REQUIRED. Single ASCII error code string.
error_description
OPTIONAL. Human-readable ASCII text description of the error used
for debugging.
Other members MAY also be included and, if they are not understood,
they MUST be ignored.
This specification defines the following error codes:
invalid_redirect_uri
The value of one or more redirection URIs is invalid.
invalid_client_metadata
The value of one of the client metadata fields is invalid and the
server has rejected this request. Note that an authorization
server MAY choose to substitute a valid value for any requested
parameter of a client's metadata.
invalid_software_statement
The software statement presented is invalid.
unapproved_software_statement
The software statement presented is not approved for use by this
authorization server.

The following is a non-normative example of an error response
resulting from a redirection URI that has been blacklisted by the
authorization server (with line breaks within values for display
purposes only):
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache
{
"error": "invalid_redirect_uri",
"error_description": "The redirection URI
http://sketchy.example.com is not allowed by this server."
}
The following is a non-normative example of an error response
resulting from an inconsistent combination of "response_types" and
"grant_types" values (with line breaks within values for display
purposes only):
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache
{
"error": "invalid_client_metadata",
"error_description": "The grant type 'authorization_code' must be
registered along with the response type 'code' but found only
'implicit' instead."
}
4. IANA Considerations
4.1. OAuth Dynamic Client Registration Metadata Registry
This specification establishes the "OAuth Dynamic Client Registration
Metadata" registry.
OAuth registration client metadata names and descriptions are
registered with a Specification Required ([RFC5226]) after a two-week
review period on the oauth-ext-review@ietf.org mailing list, on the
advice of one or more Designated Experts. However, to allow for the
allocation of names prior to publication, the Designated Experts may
approve registration once they are satisfied that such a
specification will be published, per [RFC7120].

Registration requests sent to the mailing list for review should use
an appropriate subject (e.g., "Request to register OAuth Dynamic
Client Registration Metadata name: example").
Within the review period, the Designated Experts will either approve
or deny the registration request, communicating this decision to the
review list and IANA. Denials should include an explanation and, if
applicable, suggestions as to how to make the request successful.
IANA must only accept registry updates from the Designated Experts
and should direct all requests for registration to the review mailing
list.
4.1.1. Registration Template
Client Metadata Name:
The name requested (e.g., "example"). This name is case
sensitive. Names that match other registered names in a case-
insensitive manner SHOULD NOT be accepted.
Client Metadata Description:
Brief description of the metadata value (e.g., "Example
description").
Change Controller:
For Standards Track RFCs, list "IESG". For others, give the name
of the responsible party. Other details (e.g., postal address,
email address, home page URI) may also be included.
Specification Document(s):
Reference to the document or documents that specify the client
metadata definition, preferably including a URI that can be used
to retrieve a copy of the documents. An indication of the
relevant sections may also be included but is not required.
4.1.2. Initial Registry Contents
The initial contents of the "OAuth Dynamic Client Registration
Metadata" registry are:
o Client Metadata Name: "redirect_uris"
o Client Metadata Description: Array of redirection URIs for use in
redirect-based flows
o Change Controller: IESG
o Specification Document(s): RFC 7591

o Client Metadata Name: "client_secret"
o Client Metadata Description: Client secret
o Change Controller: IESG
o Specification Document(s): RFC 7591
o Client Metadata Name: "client_id_issued_at"
o Client Metadata Description: Time at which the client identifier
was issued
o Change Controller: IESG
o Specification Document(s): RFC 7591
o Client Metadata Name: "client_secret_expires_at"
o Client Metadata Description: Time at which the client secret will
expire
o Change Controller: IESG
o Specification Document(s): RFC 7591
4.2. OAuth Token Endpoint Authentication Methods Registry
This specification establishes the "OAuth Token Endpoint
Authentication Methods" registry.
Additional values for use as "token_endpoint_auth_method" values are
registered with a Specification Required ([RFC5226]) after a two-week
review period on the oauth-ext-review@ietf.org mailing list, on the
advice of one or more Designated Experts. However, to allow for the
allocation of values prior to publication, the Designated Experts may
approve registration once they are satisfied that such a
specification will be published, per [RFC7120].
Registration requests must be sent to the oauth-ext-review@ietf.org
mailing list for review and comment, with an appropriate subject
(e.g., "Request to register token_endpoint_auth_method value:
example").
Within the review period, the Designated Experts will either approve
or deny the registration request, communicating this decision to the
review list and IANA. Denials should include an explanation and, if
applicable, suggestions as to how to make the request successful.
IANA must only accept registry updates from the Designated Experts
and should direct all requests for registration to the review mailing
list.

4.2.1. Registration Template
Token Endpoint Authentication Method Name:
The name requested (e.g., "example"). This name is case
sensitive. Names that match other registered names in a case-
insensitive manner SHOULD NOT be accepted.
Change Controller:
For Standards Track RFCs, list "IESG". For others, give the name
of the responsible party. Other details (e.g., postal address,
email address, home page URI) may also be included.
Specification Document(s):
Reference to the document or documents that specify the token
endpoint authentication method, preferably including a URI that
can be used to retrieve a copy of the document or documents. An
indication of the relevant sections may also be included but is
not required.
4.2.2. Initial Registry Contents
The initial contents of the "OAuth Token Endpoint Authentication
Methods" registry are:
o Token Endpoint Authentication Method Name: "none"
o Change Controller: IESG
o Specification Document(s): RFC 7591
o Token Endpoint Authentication Method Name: "client_secret_post"
o Change Controller: IESG
o Specification Document(s): RFC 7591
o Token Endpoint Authentication Method Name: "client_secret_basic"
o Change Controller: IESG
o Specification Document(s): RFC 7591
5. Security Considerations
Since requests to the client registration endpoint result in the
transmission of clear-text credentials (in the HTTP request and
response), the authorization server MUST require the use of a
transport-layer security mechanism when sending requests to the
registration endpoint. The server MUST support TLS 1.2 [RFC5246] and
MAY support additional transport-layer security mechanisms meeting
its security requirements. When using TLS, the client MUST perform a
TLS/SSL server certificate check, per RFC 6125 [RFC6125].
Implementation security considerations can be found in
Recommendations for Secure Use of TLS and DTLS [BCP195].

For clients that use redirect-based grant types such as
"authorization_code" and "implicit", authorization servers MUST
require clients to register their redirection URI values. This can
help mitigate attacks where rogue actors inject and impersonate a
validly registered client and intercept its authorization code or
tokens through an invalid redirection URI or open redirector.
Additionally, in order to prevent hijacking of the return values of
the redirection, registered redirection URI values MUST be one of:
o A remote web site protected by TLS
(e.g., https://client.example.com/oauth_redirect)
o A web site hosted on the local machine using an HTTP URI
(e.g., http://localhost:8080/oauth_redirect)
o A non-HTTP application-specific URL that is available only to the
client application
(e.g., exampleapp://oauth_redirect)
Public clients MAY register with an authorization server using this
protocol, if the authorization server's policy allows them. Public
clients use a "none" value for the "token_endpoint_auth_method"
metadata field and are generally used with the "implicit" grant type.
Often these clients will be short-lived in-browser applications
requesting access to a user's resources and access is tied to a
user's active session at the authorization server. Since such
clients often do not have long-term storage, it is possible that such
clients would need to re-register every time the browser application
is loaded. To avoid the resulting proliferation of dead client
identifiers, an authorization server MAY decide to expire
registrations for existing clients meeting certain criteria after a
period of time has elapsed. Alternatively, such clients could be
registered on the server where the in-browser application's code is
served from, and the client's configuration could be pushed to the
browser alongside the code.
Since different OAuth 2.0 grant types have different security and
usage properties, an authorization server MAY require separate
registrations for a piece of software to support multiple grant
types. For instance, an authorization server might require that all
clients using the "authorization_code" grant type make use of a
client secret for the "token_endpoint_auth_method" but any clients
using the "implicit" grant type not use any authentication at the
token endpoint. In such a situation, a server MAY disallow clients
from registering for both the "authorization_code" and "implicit"
grant types simultaneously. Similarly, the "authorization_code"
grant type is used to represent access on behalf of an end-user, but
the "client_credentials" grant type represents access on behalf of
the client itself. For security reasons, an authorization server
could require that different scopes be used for these different use

cases, and, as a consequence, it MAY disallow these two grant types
from being registered together by the same client. In all of these
cases, the authorization server would respond with an
"invalid_client_metadata" error response.
Unless used as a claim in a software statement, the authorization
server MUST treat all client metadata as self-asserted. For
instance, a rogue client might use the name and logo of a legitimate
client that it is trying to impersonate. Additionally, a rogue
client might try to use the software identifier or software version
of a legitimate client to attempt to associate itself on the
authorization server with instances of the legitimate client. To
counteract this, an authorization server MUST take appropriate steps
to mitigate this risk by looking at the entire registration request
and client configuration. For instance, an authorization server
could issue a warning if the domain/site of the logo doesn't match
the domain/site of redirection URIs. An authorization server could
also refuse registration requests from a known software identifier
that is requesting different redirection URIs or a different client
URI. An authorization server can also present warning messages to
end-users about dynamically registered clients in all cases,
especially if such clients have been recently registered or have not
been trusted by any users at the authorization server before.
In a situation where the authorization server is supporting open
client registration, it must be extremely careful with any URL
provided by the client that will be displayed to the user (e.g.,
"logo_uri", "tos_uri", "client_uri", and "policy_uri"). For
instance, a rogue client could specify a registration request with a
reference to a drive-by download in the "policy_uri", enticing the
user to click on it during the authorization. The authorization
server SHOULD check to see if the "logo_uri", "tos_uri",
"client_uri", and "policy_uri" have the same host and scheme as the
those defined in the array of "redirect_uris" and that all of these
URIs resolve to valid web pages. Since these URI values that are
intended to be displayed to the user at the authorization page, the
authorization server SHOULD protect the user from malicious content
hosted at the URLs where possible. For instance, before presenting
the URLs to the user at the authorization page, the authorization
server could download the content hosted at the URLs, check the
content against a malware scanner and blacklist filter, determine
whether or not there is mixed secure and non-secure content at the
URL, and other possible server-side mitigations. Note that the
content in these URLs can change at any time and the authorization
server cannot provide complete confidence in the safety of the URLs,
but these practices could help. To further mitigate this kind of
threat, the authorization server can also warn the user that the URL
links have been provided by a third party, should be treated with

caution, and are not hosted by the authorization server itself. For
instance, instead of providing the links directly in an HTML anchor,
the authorization server can direct the user to an interstitial
warning page before allowing the user to continue to the target URL.
Clients MAY use both the direct JSON object and the JWT-encoded
software statement to present client metadata to the authorization
server as part of the registration request. A software statement is
cryptographically protected and represents claims made by the issuer
of the statement, while the JSON object represents the self-asserted
claims made by the client or developer directly. If the software
statement is valid and signed by an acceptable authority (such as the
software API publisher), the values of client metadata within the
software statement MUST take precedence over those metadata values
presented in the plain JSON object, which could have been intercepted
and modified.
Like all metadata values, the software statement is an item that is
self-asserted by the client, even though its contents have been
digitally signed or MACed by the issuer of the software statement.
As such, presentation of the software statement is not sufficient in
most cases to fully identify a piece of client software. An initial
access token, in contrast, does not necessarily contain information
about a particular piece of client software but instead represents
authorization to use the registration endpoint. An authorization
server MUST consider the full registration request, including the
software statement, initial access token, and JSON client metadata
values, when deciding whether to honor a given registration request.
If an authorization server receives a registration request for a
client that is not intended to have multiple instances registered
simultaneously and the authorization server can infer a duplication
of registration (e.g., it uses the same "software_id" and
"software_version" values as another existing client), the server
SHOULD treat the new registration as being suspect and reject the
registration. It is possible that the new client is trying to
impersonate the existing client in order to trick users into
authorizing it, or that the original registration is no longer valid.
The details of managing this situation are specific to the
authorization server deployment and outside the scope of this
specification.
Since a client identifier is a public value that can be used to
impersonate a client at the authorization endpoint, an authorization
server that decides to issue the same client identifier to multiple
instances of a registered client needs to be very particular about
the circumstances under which this occurs. For instance, the
authorization server can limit a given client identifier to clients

using the same redirect-based flow and the same redirection URIs. An
authorization server SHOULD NOT issue the same client secret to
multiple instances of a registered client, even if they are issued
the same client identifier, or else the client secret could be
leaked, allowing malicious impostors to impersonate a confidential
client.
6. Privacy Considerations
As the protocol described in this specification deals almost
exclusively with information about software and not people, there are
very few privacy concerns for its use. The notable exception is the
"contacts" field as defined in Section 2, which contains contact
information for the developers or other parties responsible for the
client software. These values are intended to be displayed to end-
users and will be available to the administrators of the
authorization server. As such, the developer may wish to provide an
email address or other contact information expressly dedicated to the
purpose of supporting the client instead of using their personal or
professional addresses. Alternatively, the developer may wish to
provide a collective email address for the client to allow for
continuing contact and support of the client software after the
developer moves on and someone else takes over that responsibility.
In general, the metadata for a client, such as the client name and
software identifier, are common across all instances of a piece of
client software and therefore pose no privacy issues for end-users.
Client identifiers, on the other hand, are often unique to a specific
instance of a client. For clients such as web sites that are used by
many users, there may not be significant privacy concerns regarding
the client identifier, but for clients such as native applications
that are installed on a single end-user's device, the client
identifier could be uniquely tracked during OAuth 2.0 transactions
and its use tied to that single end-user. However, as the client
software still needs to be authorized by a resource owner through an
OAuth 2.0 authorization grant, this type of tracking can occur
whether or not the client identifier is unique by correlating the
authenticated resource owner with the requesting client identifier.
Note that clients are forbidden by this specification from creating
their own client identifier. If the client were able to do so, an
individual client instance could be tracked across multiple colluding
authorization servers, leading to privacy and security issues.
Additionally, client identifiers are generally issued uniquely per
registration request, even for the same instance of software. In
this way, an application could marginally improve privacy by
registering multiple times and appearing to be completely separate

Appendix A. Use Cases
This appendix describes different ways that this specification can be
utilized, including describing some of the choices that may need to
be made. Some of the choices are independent and can be used in
combination, whereas some of the choices are interrelated.
A.1. Open versus Protected Dynamic Client Registration
A.1.1. Open Dynamic Client Registration
Authorization servers that support open registration allow
registrations to be made with no initial access token. This allows
all client software to register with the authorization server.
A.1.2. Protected Dynamic Client Registration
Authorization servers that support protected registration require
that an initial access token be used when making registration
requests. While the method by which a client or developer receives
this initial access token and the method by which the authorization
server validates this initial access token are out of scope for this
specification, a common approach is for the developer to use a manual
preregistration portal at the authorization server that issues an
initial access token to the developer.
A.2. Registration without or with Software Statements
A.2.1. Registration without a Software Statement
When a software statement is not used in the registration request,
the authorization server must be willing to use client metadata
values without them being digitally signed or MACed (and thereby
attested to) by any authority. (Note that this choice is independent
of the Open versus Protected choice, and that an initial access token
is another possible form of attestation.)
A.2.2. Registration with a Software Statement
A software statement can be used in a registration request to provide
attestation by an authority for a set of client metadata values.
This can be useful when the authorization server wants to restrict
registration to client software attested to by a set of authorities
or when it wants to know that multiple registration requests refer to
the same piece of client software.

A.3. Registration by the Client or Developer
A.3.1. Registration by the Client
In some use cases, client software will dynamically register itself
with an authorization server to obtain a client identifier and other
information needed to interact with the authorization server. In
this case, no client identifier for the authorization server is
packaged with the client software.
A.3.2. Registration by the Developer
In some cases, the developer (or development software being used by
the developer) will preregister the client software with the
authorization server or a set of authorization servers. In this
case, the client identifier value(s) for the authorization server(s)
can be packaged with the client software.
A.4. Client ID per Client Instance or per Client Software
A.4.1. Client ID per Client Software Instance
In some cases, each deployed instance of a piece of client software
will dynamically register and obtain distinct client identifier
values. This can be advantageous, for instance, if the code flow is
being used, as it also enables each client instance to have its own
client secret. This can be useful for native clients, which cannot
maintain the secrecy of a client secret value packaged with the
software, but which may be able to maintain the secrecy of a per-
instance client secret.
A.4.2. Client ID Shared among All Instances of Client Software
In some cases, each deployed instance of a piece of client software
will share a common client identifier value. For instance, this is
often the case for in-browser clients using the implicit flow, when
no client secret is involved. Particular authorization servers might
choose, for instance, to maintain a mapping between software
statement values and client identifier values, and return the same
client identifier value for all registration requests for a
particular piece of software. The circumstances under which an
authorization server would do so, and the specific software statement
characteristics required in this case, are beyond the scope of this
specification.

A.5. Stateful or Stateless Registration
A.5.1. Stateful Client Registration
In some cases, authorization servers will maintain state about
registered clients, typically indexing this state using the client
identifier value. This state would typically include the client
metadata values associated with the client registration, and possibly
other state specific to the authorization server's implementation.
When stateful registration is used, operations to support retrieving
and/or updating this state may be supported. One possible set of
operations upon stateful registrations is described in [RFC7592].
A.5.2. Stateless Client Registration
In some cases, authorization servers will be implemented in a manner
the enables them to not maintain any local state about registered
clients. One means of doing this is to encode all the registration
state in the returned client identifier value, and possibly
encrypting the state to the authorization server to maintain the
confidentiality and integrity of the state.
Acknowledgments
The authors thank the OAuth Working Group, the User-Managed Access
Working Group, and the OpenID Connect Working Group participants for
their input to this document. In particular, the following
individuals have been instrumental in their review and contribution
to various draft versions of this document: Amanda Anganes, Derek
Atkins, Tim Bray, Domenico Catalano, Donald Coffin, Vladimir
Dzhuvinov, George Fletcher, Thomas Hardjono, William Kim, Torsten
Lodderstedt, Eve Maler, Josh Mandel, Nov Matake, Tony Nadalin, Nat
Sakimura, Christian Scholz, and Hannes Tschofenig.